The present disclosure relates generally to handheld power tools, and specifically to fastener driving tools, including, but not limited to combustion-powered fastener-driving tools, also referred to as combustion tools or combustion nailers, as well as pneumatic nailers and electric milers employing reciprocating driving elements and magazine feeders.
Combustion-powered tools are known in the art, and one type of such tools, also known as IMPULSE® brand tools for use in driving fasteners into workpieces, is described in commonly assigned patents to Nikolich U.S. Pat. Re. No. 32,452, and U.S. Pat. Nos. 4,522,162; 4,483,473; 4,483,474; 4,403,722; 5,197,646; 5,263,439; 6,145,724 and 7,341,171, all of which are incorporated by reference herein. Similar combustion-powered nail and staple driving tools are available commercially from ITW-Paslode of Vernon Hills, Ill. under the IMPULSE®, BUILDEX® and PASLODE® brands.
Such tools incorporate a tool housing enclosing a small internal combustion engine. The engine is powered by a canister of pressurized fuel gas, also called a fuel cell. A battery-powered electronic power distribution unit produces a spark for ignition, and a fan located in a combustion chamber provides for both an efficient combustion within the chamber, while facilitating processes ancillary to the combustion operation of the device. The engine includes a reciprocating piston with a driving element, preferably an elongated, rigid driver blade disposed within a single cylinder body. A resilient bumper is located at the bottom of the cylinder. Fasteners are fed magazine-style into the nosepiece, where they are held in a properly positioned orientation for receiving the impact of the driving element.
When the user depresses the tool against a workpiece, the tool closes the combustion chamber and fuel is delivered into the combustion chamber. After fuel/air mixing, the user activates the trigger, initiating a spark with the ignition spark unit, then the burnt gas generates a high pressure to push the piston down and drive the nail. Just prior to the piston impacting the bumper, the piston passes through the exhaust port, and some of the gas is exhaust. The tool structure absorbs heat from the remaining combusted gasses and generates vacuum pressure to retract the piston hack to the pre-firing position. Simultaneously, the fastener feeding mechanism feeds the next fastener into a pre-driving position in the nosepiece or nose (the terms are considered interchangeable). After the piston returns to the pre-firing position, the combustion chamber is opened to scavenge air for the next cycle.
One design requirement of conventional tools is that materials are selected for their heat conduction and dissipation properties. Typically, the cylinder and reciprocating valve sleeve, which largely defines the combustion chamber, are made of cast aluminum alloy, which is formed with a plurality of cooling fins for facilitating the dissipation of heat absorbed from repeated use. The use of such alloys, while considered necessary for the management of heat generated during extended tool operation, also results in a relatively heavy tool. As is well known, heavier tools result in operator fatigue after extended operation.
Another design factor of conventional combustion nailers is that the combustion chamber should remain closed, momentarily, after combustion to make sure the pressure differential in the tool is maintained for achieving piston return to the prefiring position, so that another fastener may be driven. Due to a variety of factors, including but not limited to the speed of the operator in driving fasteners, premature opening of the combustion chamber, and in some cases friction caused by the feeding mechanism urging fasteners against the driver blade, the return of the piston to the prefiring position is slowed or even stopped. While various combustion chamber lockout systems have been proposed, there is an ongoing focus on achieving proper and rapid piston return after firing.
Thus, there is a need for a combustion tool, which more effectively manages heat generated during extended use, and there is also a need for improving combustion trailers so that after firing, the drive piston is properly returned to the prefiring position.